Arpimedes is a funky little arpeggiator plugin with adjustable pattern rhythm and speed.

You can define the number of octaves it should use and the step length of the current pattern. Of course several different arp modes are included. And you can even sync the arpeggiator to your host sequencer's tempo !

Doesn't work with Ableton or LMMS. Although, I expect it works with Logic Pro and/or Garageband. Extremely disappointed for the incompatibility however, it's not the developer's fault. Ableton doesn't support third-party MIDI FX plugins and LMMS just doesn't do third-party plugins (which is weird because as it is open-source, making it pretty much all, itself, third-party).